Forensic entomology frequently assists forensic medicine in legal investigations. It makes it possible to estimate the time of death when a cadaver is recovered at a relatively advanced stage of decomposition. In criminalistics practice, unburied bodies are found the most commonly, and therefore the fauna of these cadavers is the best investigated. The aim of this study was to collect a succession of insects and other invertebrates occurring on an unburied corpse. The experiment was conducted on the carcass of a cat euthanized due to an advanced cancer process. The carcass was colonized by three phyla of animals: Annelidae, Mollusca, and Arthropoda. They belonged to 7 classes and 10 orders. The most diverse were Arthropoda. They were classified into 5 classes: Insecta, Diplopoda, Malacostraca, Entognata, and Arachnida, and into 8 orders: Julida, Isopoda, Collembola, Diptera, Coleoptera, Hemiptera, Araneae, and Acari. The fly species Calliphora vicina from the family Calliphoridae is of particular interest among the insects collected because it is one of the fundamental indicator species whose life cycle makes it possible to determine an approximate time of death. During the study it was noted that arthropods occurred in a certain pattern of succession, predictable in forensic entomology. The first group was Calliphora vicina (Calliphoridae, Diptera), which laid eggs. The next (second) group consisted of first-instar C. vicina larvae and insects feeding on these larvae, such as Philonthus tenuicornis (Staphylinidae, Coleoptera). The first stage of succession was the appearance of eggs of C. vicina. The second phase was the appearance of adult flies other than Calliphoridae and of accidental species, as well as beetles (e.g. Philonthus tenuicornis, Staphylinidae, Coleoptera) feeding on larvae of C. vicina. The third phase of succession was the appearance of all larvae stages of C. vicina that continued and finished their life cycle.